(i) Field of the Invention
This invention relates to a novel flexible floating boom for containing surface contaminants on bodies of water. In particular it relates to an oil containment boom having the floating means disposed therewithin and to a novel method for containing oil spills in ice-infested waters.
(II) Description of the Prior Art
With the tremendous rate of industrialization that is taking place throughout the world, pollution of bodies of water by oil spills is reaching critical proportions. Not only are major oil spills occurring, such as, for example, when an oil tanker is wrecked, but also minor oil spills are a daily occurrence throughout the world. Many different systems are being tested for removing the effects of these oil spills and one of the most successful techniques has been to contain these spills by means of booms and then to collect the contained oil from the surface of the water, e.g., by skimmers. Such oil booms can be used not only for containing a major oil spill but can also be used for isolating terminals from a permanent installation, temporarily encircling tankers which are being loaded and unloaded, sweeping port areas for removing floating patches of oil, protecting beaches, etc. In order to provide the necessary versatility, these oil booms must be inexpensive, light and easy to store and handle.
One such oil boom is in the form of a flexible fabric curtain wall which floats in the water with part of the curtain wall extending a distance below the water surface and a part extending above the water surface. Some of these flexible booms are supported in the water by means of separately attached floats. Spaced vertical stiffeners are provided to maintain the boom in the necessary vertical position and they are stabilized by means of weights along the bottom submerged edge. These booms are made up and stored in convenient sections, e.g. of about 100 feet in length, and when needed are attached together and deployed in the water to surround and contain the oil spill.
When such booms are used in adverse sea and wind conditions, there is a tendency for them to fail because of tearing under the strain of the sea or ice conditions and also a tendency for the attached floats to be torn away, or damaged, thus allowing the boom to become submerged in certain areas and consequently defeating the entire purpose of trying totally to contain the oil spill. Accordingly, there is a very great need for a flexible oil boom system which will be very inexpensive to produce, easy to handle and yet have sufficient strength to withstand adverse sea and wind conditions as well as to withstand any serious damage from ice floating on the surface of the water.
Canadian Patent No. 906,772 attempted to solve such problem by providing a flexible oil boom comprising a curtain wall of sheet material having an upper portion and a lower portion. These upper and lower portions were joined together by an overlapping connection at a location below the water line. At spaced locations along the length of the joint between the upper and lower portions, flexible straps were positioned, which surrounded the lower edge of the upper portion and passed through the overlapping connection between the upper and lower portions so that the straps provided extending ends on either side of the boom. These straps were used for connecting the float members to the boom. The upper edge of the boom was preferably formed with a longitudinal pocket which contained a strengthening rope and a similar longitudinal pocket with strengthening rope was also preferably provided at the bottom edge. Vertical pockets were also provided along the boom at longitudinally spaced positions and these pockets contained stiffening members for holding the boom in a vertically upright position.
It is, moreover, frequently necessary to skim oil slicks in harbour areas. However, present skimmers encounter considerable resistance in being towed through the water and are difficult to handle. It has also become desirable to contain oil slicks resulting from underwater leaks or leaks from injured vessels. However, the great majority of boom systems proposed for such use do not survive long in rough seas. In addition, many of the more rigid boom systems do not conform to the contours of the waves sufficiently fast to prevent the passage of oil beneath sections which are left hanging in the air.
Canadian Pat. No. 912,293 attempted to provide a solution to such problem by providing a flexible boom comprising at least one elongated flexible floatation unit, a flexible weighted net supported in a substantially vertical position by that at least one elongated floatation unit when the boom was placed in a body of water, and at least one layer of flexible filtering material, that layer of flexible filtering material being associated with the weighted net to conform generally to the vertical positioning and movement of the weighted net. The layer of filtering material was formed of hydrophobic, oleophilic material having a plurality of passageways therethrough permitting the flow of water through the boom while substantially preventing the flow of liquid hydrocarbonaceous matter through the boom.
Another problem attendant in the use of such booms is that the basically heavy and bulky nature of such known booms make both the storage and handling thereof difficult. By the same token, notwithstanding the weight and bulk of these retainers, such often incorporate a relatively low tensile strength, both in the individual sections and in the joining portions, thus limiting the lengths which can be effectively used, both as a standing barrier and as a towed gathering unit.
Canadian Pat. No. 912,294 attempted to provide a solution to such problem by providing such a boom comprising an elongated depending skirt having upper and lower edges, with a float section defined longitudinally along the upper edge of the skirt, and a ballast section defined longitudinally along the lower edge of the skirt. A first male joining end was defined at one end of the retainer, and a second female joining end was defined at the second end of the retainer, the female joining end being of a size and configuration so as telescopically to receive the male end of an adjoining retainer. Means were associated with the ends for interconnecting a pair of telescoped ends, such retainer being formed of an elongated flexible sheet longitudinally folded to define a skirt forming pair of adjacent panels bounded along the upper edge by a longitudinally extending enlarged pocket constituting a portion of the float section. A relatively smaller longitudinally extending second pocket was provided along the lower edges of the panel for the reception of ballast. The second pocket constituted a portion of the ballast section. Means were provided for securing the skirt defining panels together along substantially the full length thereof. Float means were received within the first mentioned pocket, the float means, ballast and securing means terminating short of the second female joining end for enabling the reception of the first male joining end therein. A pair of cooperating securing collars was provided, one collar being mounted on and surrounding the float section adjacent each end of the retainer. The collars each had an inner edge fixed to the float section and an unsecured outer edge directed toward the corresponding end of the retainer. The collars were adapted telescopically to engage with the corresponding collars on adjacent retainers upon an interengagement of the male and female joining ends thereon. Means were associated with the collars for interconnecting a pair of telescoped collars.
Other problems are inherent in the use of such oil barriers. The oil slick may vary from a mere fraction of an inch up to a foot or more in thickness. Therefore the barrier must extend to a sufficient depth to avoid the passing of the oil beneath the barrier; the probability of this passing of oil is increased by the action of each of the waves and swells of normal sea action or as caused by passing vessels, including large cargo ships and ocean liners. However, as the depth of the barrier increases, a larger float is required, and particularly a material of substantially greater strength is required which will withstand the great force of wave and swell action as well as withstand the bombardment by miscellaneous trash-missiles, for example including objects up to the size of telephone poles.
Another problem arises from the fact that many materials tend to sink or to disintegrate when they become saturated with oil or water. Oil in particular results in extensive degradation. Thus the material must remain afloat, and must be oil-resistant.
Another problem is that an oil barrier which might overcome some of the above and other problems would normally be highly expensive, complex, and too bulky to be of practical value in most instances.
Canadian Pat. No. 914,435 attempted to solve such problem by providing a buoyant barrier boom comprising a substantially rigid sheet-structure comprising a first sheet of a substantially oil-resistant synthetic composition and closed-cell foam composition attached to the sheet-structure in a manner whereby that sheet-structure floated when placed in water in a substantially vertical position relative to the water's surface. About one-eighth to about two-thirds of the first sheet extended above the water surface by at least about 0.5 foot, and extended below the water's surface at least a sufficient depth (at least about one foot) to maintain the sheet in the substantially vertical position.
Yet another problem inherent in the use of such floating booms was that some such booms allowed oil to escape both under and over the boom when used in the open sea or in rough water due to the wave action and instability of the boom.
Canadian Pat. No. 936,372 purported to solve such problem by providing a floating boom comprising a plurality of connector cables, and a plurality of upright support members attached to the connector cables, the upright support members having a first curved end portion inwardly disposed towards the oil spill being contained or collected and a second weighted end portion. A buoyant support tube was attached to the upright support member, the buoyant support tube having a valve means for inflating the buoyant support tube with compressed gas from a source of such gas. A barricade wall material was provided for collecting and containing the oil attached to the upright support members. The connector cables were adapted to be attached to at least one seagoing vessel to position the floating boom around an oil spill to form an oil barricade to contain or collect the oil spill.
(iii) Particular Problems with the Prior Art
Moreover, nowhere is the threat to the environment more acute than in the northern oceans where rough seas and heavy ice conditions increase the magnitude of the problems associated with controlling oil spils, and where potential damage to the environment may have lasting and sever implications.
Although as described above numerous oil containment booms have been proposed, none are able to cope with conditions encountered in ice-infested, choppy water, and in areas where there is dominant breaking wave action by the seas forming white-capped waves.
One of the problems with booms in steep choppy waves is the difficulty in making a boom respond quickly to such fast rising waves. Even if the boom follows the wave itself, it is almost impossible to make it respond to the breaking whitecap and have it buoyant enough to rise fast and high enough to keep above and catch the whitecap which is of less density, containing both water and air. Consequently, such waves have a tendency to break over normal booms, carrying oil with them.
It has been found further that, in ice, a boom with external tension lines and with external floating attachments traps ice bearing down on it and, being unable to release the pressure exerted by the drifting ice, allows forces to build up until either the boom or the mooring system breaks, thereby making the boom ineffective.